Unfortunately, vandals have increasingly been turning to glass etchants as a tool of choice for graffiti. For example, graffiti on glass windows of subway cars is commonplace. Vandals have been forming such graffiti on windows of subway cars, buildings, trains, buses and other glass windows by using glass etchants which are capable of etching glass at locations where such etchants are applied.
Armor-etch is an example of a bifluoride salt (e.g., ammonia bifluoride or sodium bifluoride) based paste used for etching patterns on glass surfaces, and has been used in forming graffiti. The mechanism of fluoride ion attack on SiO2 of glass is summarized below for purposes of example only and understanding.
Though hydrogen fluoride (HF) does not dissociate well, active hydrogen fluoride paste reacts with silicate (which forms the matrix for glass) in the presence of water as in the following equations:HF2—=HF+F—6HF+SiO2=H2SiF6+2H2O
An alternative type of glass etching material, which is also a bi-fluoride based etchant, is sometimes referred to as B&B etching crème manufactured by B&B Etching Products. Ammonium bifluoride ((NH4)HF2) and sodium bifluoride (NaHF2) salts are very soluble in water. For example, a 2.8 g/100 g solution of ammonium fluoride would produce a 1.7 g/100 g solution of hydrofluoric acid (HF) at pH 1, with 85% of the fluorine atoms in the form of HF. At higher concentrations or higher pH, a significant amount of the HF2− ion is present. Acidified fluorides can produce substantial quantities of HF in solution.
The active ammonia bi-fluoride reacts with silicate in the presence of water as presented in the following equations:(NH4)HF2=(NH4)++HF2—HF2—=HF+F—6HF+SiO2=H2SiF6+2H2O
An equilibrium is established between the reactants and products. Thus, as hydrogen fluoride is consumed in reacting with the SiO2 of the glass, more hydrogen fluoride is produced to maintain the equilibrium. The SiO2 etch rate (i.e., the etch rate of the glass) is linearly related to the HF— and HF2− concentrations, and is not related to the F— concentration at any pH.
Conventional coatings used for fluoride resistance to protect glass from such etchings are polymer-based film. Unfortunately, these coatings are susceptible to damage and are not scratch resistant thereby rendering their use in environments such as subway cars, buses and vehicles undesirable. Moreover, in some cases the film can be lifted and the etchant applied under the film.
Scratch resistant coated glass articles are known which utilize a layer(s) comprising diamond-like carbon (DLC) on the glass surface. For example, see U.S. Pat. Nos. 6,261,693, 6,303,226, 6,280,834, 6,284,377, 6,447,891, 6,461,731, 6,395,333, 6,335,086, and 6,592,992, the disclosures of which are all hereby incorporated herein by reference. While carbon is resistant to fluoride ion (and HF2—) attack, these layers when formed via ion beam deposition techniques at very small thicknesses give rise to micro-particulates on the substrate. When such layers are very thin in nature, these micro-particles may give rise to pinholes which are pathways for the HF to attack the underlying glass. Thus, scratch resistant coated articles which utilize only a layer comprising DLC on the glass are sometimes susceptible to the fluoride based etchant attacks described above.
In view of the above, it can be seen that there exists a need in the art for a scratch resistant coated article which is also resistant to attacks by fluoride-based etchant(s).
A scratch resistant coated article is provided which is also resistant to attacks by at least some etchants (e.g., fluoride-based etchant(s)) for at least a period of time. In certain example embodiments, an anti-etch layer(s) is provided on the glass substrate in order to protect the glass substrate from attacks by fluoride-based etchant(s). In certain example embodiments, the anti-etch layer(s) is substantially transparent to visible light.
In certain example embodiments of this invention, the anti-etch layer may be provided on the substrate over an underlayer(s) of a dielectric material. In certain example embodiments, the dielectric underlayer may be formed using flame pyrolysis in an atmosphere at or close to atmospheric pressure. The use of flame pyrolysis to form the underlayer(s) is advantageous in that the layer(s) formed using flame pyrolysis may be formed in an ambient atmosphere which need not be at a pressure less than atmospheric (as opposed to sputtering for example which is typically formed in a chamber at a low pressure less than atmospheric). Thus, expensive sputtering or other low-pressure deposition systems need not be used to form this particular layer(s). Moreover, another example advantage is that such an underlayer deposited via flame pyrolysis has been found to further improve the etch resistance of the coated article by removing or reducing chemical or other defects on the glass surface. In particular, it is believed that the flame-pyrolysis deposited underlayer removes or reduces chemical defects on the surface on which the anti-etch layer is directly provided. Such defects may lead to growth defects in the anti-etch layer 2 which can be weak points more susceptible to etchant attack. Thus, the removal or reduction of such defects via the use of the flame pyrolysis deposited underlayer is advantageous in that etch resistance can be surprisingly improved.
In certain example embodiments, the anti-etch layer may be provided on the glass substrate, along with an overlying scratch resistant layer of or including diamond-like carbon (DLC). The anti-etch layer may be of or include any suitable material such as, for example, the material(s) discussed herein.
In certain example embodiments, the anti-etch layer(s) may comprise or consist essentially of zirconium oxycarbide, hydrogenated zirconium oxycarbide, tin oxycarbide, or hydrogenated tin oxycarbide. In certain example embodiments, the optional underlayer(s) may comprise or consist essentially of silicon oxide, silicon nitride, and/or the like.
In certain example embodiments, there is provided a method of making a coated article, the method comprising providing a glass substrate; using flame pyrolysis to deposit at least one layer on the glass substrate; and forming an anti-etch layer on the glass substrate over the flame pyrolysis deposited layer.
In other example embodiments of this invention, there is provided a coated article comprising a substrate; an underlayer comprising silicon oxide on the substrate; and an anti-etch layer comprising at least one material selected from the group consisting of: zirconium oxycarbide, tin oxycarbide, indium oxide and cerium oxide; and wherein the anti-etch layer is on the substrate over at least the underlayer comprising silicon oxide, and wherein the anti-etch layer is resistant to at least some fluoride-based glass etchants.
In certain example embodiments, a method of making a coated article is provided. A glass substrate is provided. An anti-etch layer is formed on the glass substrate, with the anti-etch layer comprising at least one of fluorine-doped tin oxide and cerium oxide. A scratch-resistant layer comprising diamond-like carbon (DLC) is ion beam deposited on the glass substrate over the anti-etch layer. A seed layer is formed between the anti-etch layer and the layer comprising DLC, with the seed layer facilitating adhesion of the layer comprising DLC and/or protecting the anti-etch layer from damage during the ion beam depositing of the layer comprising DLC.
In certain example embodiments, a method of making a coated article is provided. A glass substrate is provided. A base layer or underlayer is formed on the glass substrate. An anti-etch layer is formed over the base layer or underlayer, with the anti-etch layer comprising at least one of fluorine-doped tin oxide and cerium oxide. A layer comprising diamond-like carbon (DLC) is ion beam deposited on the glass substrate over the anti-etch layer. A seed layer is formed between the anti-etch layer and the layer comprising DLC, with the seed layer comprising silicon nitride.
In certain example embodiments, a coated article is provided. The coated article comprises a glass substrate; an anti-etch layer formed on the glass substrate, with the anti-etch layer comprising fluorine-doped tin oxide and/or cerium oxide; an ion beam deposited scratch-resistant layer comprising diamond-like carbon (DLC) on the glass substrate over the anti-etch layer; and a seed layer provided between the anti-etch layer and the layer comprising DLC, with the seed layer cooperating with the layer comprising DLC to facilitate adhesion of the layer comprising DLC and/or to protect the anti-etch layer from damage during the ion beam depositing of the layer comprising DLC.
The features, aspects, advantages, and example embodiments described herein may be combined to realize yet further embodiments.